If you use the REST button to get into live data, you can look at AC system pressure. There are charts for R134 temperature Vs pressure. This won't tell you if the system is fully charged, just if there is something in there. However, since you got a pressure sensor code, that tells me that the sensor has failed, is unplugged , has wiring issue , control head is bad.

When a liquid changes to a gas in a sealed container, the pressure will stabilize based on temperature. You could have a few drops of liquid or a quart and the pressure would be the same.